1. Field of the Invention
This invention relates to a data transmission system in which a plurality of repeater nodes are interconnected by transmission links and, more particularly, to a system that has a predetermined bypass path split ratio and does not require an automatic gain control circuit.
2. Description of the Related Art
Fault tolerant systems for data transmission systems are known in the art. Conventional methods for providing fault tolerant systems include methods which bypass the main transmission path utilizing a bypass switch which, upon failure at a node, will allow a bypass around the failed node. Another method utilizes parallel redundant transmission equipment, thereby allowing use of a secondary system when a primary system fails. Chown et al., U.S. Pat. No. 4,166,946, teaches a data transmission system utilizing optical fibers in which an optical fiber bypass arrangement is provided in the event of a repeater node failure. In each of the above systems, the main signal input into the repeater is boosted and sent further down the line. This boosting is needed to cure the effect of signal degradation as the signal travels over the transmission line.
FIG. 1 is a graph conceptually showing how a repeater of the prior art affects a signal applied to its input. As shown in FIG. 1, a digital signal (line A), which has degraded due to propagation losses, is applied to the input. In the repeater, the signal is boosted by adding to the input signal (portion C in FIG. 1), thus raising the amplitude of the signal so that it is output as shown by dotted line B. A major problem in implementing such a boosting scheme is the accuracy by which the boosted signal is added to the original signal. Also, an optically incoherent boost scheme cannot improve the accumulation of pulse dispersion.